Phase Transition of Thermally Treated Polyhedral Nano Nickel Oxide with Reduced Band Gap

Abstract

Nickel oxide (NiO) is a semiconducting material which exhibits a unique electronic structure. Because of its distinctive electronic properties, NiO stands as an intriguing candidate for various applications in optoelectronics, photo catalysis, and energy devices such as solar cells. In the present work efforts have been made to tailor the band gap of NiO. A simple co-precipitation method followed by heat treatment is utilized to synthesize the material. Prior to heat treatment, x-ray diffraction study of the as synthesized material showed the presence of nickel hydroxide [Ni(OH)2]. On calcination for one hour at 1000oC, a single phase NiO wasrevealed. After heat treatment it was noticed that the particle size was found to be increased. The absorption spectra of [Ni(OH)2] and NiO were recorded using UV-Vis spectroscopy method. Using Tauc plot a band gap of 4.2 eV and 1.8 eV for Ni(OH)2 and NiO was observed respectively. It is observed that a significant decrease in band gap of NiO was noticed. Surface morphological study was carried out by using FESEM, which revealed the transformation of sheet like structures of [Ni(OH)2] to polyhedral shaped NiO on calcination. The presence of nickel and oxygen was confirmed by the energy dispersive spectrometry analysis.